This invention relates to an ink transfer material for printers, and more particularly to an ink transfer material which is excellent in dimensional stability and durability, virtually free from plastic deformation, and useful for typewriters and other similar impact printers and thermal transfer printers.
Polyester film is utilized as the substrate of an ink transfer material for printers because this film possesses outstanding properties such as high crystallinity, a high melting point, excellent thermostability and chemical resistance, high tensile and impact strengths, and high tensile modulus.
The ink transfer material, when used in impact printers such as typewriters, is required to endure tension and printing pressure and warrant repeated use. In thermal transfer printers, the extremely thin substrates are required to increase thermal conductivity. Therefore, the substrates for the ink transfer material are required to possess high tensile and impact strengths and small deformation including thermal shrinkage.
In the ink transfer material using an ordinary biaxially oriented polyester film as the substrate thereof, however, there often occurs problems of longitudinal elongation and plastic deformation in dotted parts during the transfer of ink, therefore it is unsatisfactory for a printer ribbon which is quite susceptible of high tension and high printing pressure.
The ink transfer material using the typical biaxially oriented polyester film available on the market is embossed under the impacts of printing types and, because of the prominent and persistent projections left in the film, is not smoothly rewound in the spool or the cassette of a limited capacity.
The plastic deformation or embossing is caused by the property of the film whereby it is distorted under impact pressure and does not return to be flat, after the impact pressure is released.
The ink transfer material for the thermal transfer printers is desired to be a good thermal conductivity and, therefore, is expected to use a thin substrate as far as possible. If the ordinary biaxially oriented polyester thin film available on the market is used as the substrate, it still fails to make a satisfactory ink transfer material for thermal transfer printers because of insufficient tensile strength.
When the ordinary tensilized polyester film whose F-5 value in the longitudinal direction exceeds 16 kg/mm.sup.2 is used as the substrate of an ink transfer material for impact printers, the film is liable to sustain tear in the longitudinal direction during ink transfer by impact printer, and as the substrate of an ink transfer material for thermal printers, its thermal shrinkage is too large to make it useful.